python快速排序的运作过程

# 快速排序-递归

def quick_sort(alist, begin, end):

    # 递归的终止条件是begin >= last,即数组大小为1或0

    # 递归终止时，数组已经排好序了

    if begin >= end:

        return

    else:

        # 以开头的值作为基准值，然后以基准值为界将数组分区，将分区后的左右两部分继续调用快速排序函数

        mid_value = alist[begin]

        low = begin

        high = end

        # 分别从右往左寻找小于基准值的值，从左往右寻找大于基准值的值

        while low < high:

            # 从右往左寻找小于基准值的值

            while low < high and alist[high] >= mid_value:

                high -= 1

            alist[low] = alist[high]

            # 从左往右寻找大于基准值的值

            while low < high and alist[low] < mid_value:

                low += 1

            alist[high] = alist[low]

        # 循环结束时，low == high，这个位置正是基准点的位置

        alist[low] = mid_value

        # 对low左边的元素执行快速排序

        quick_sort(alist, begin, low - 1)

        quick_sort(alist, low + 1, end)

if __name__ == '__main__':

    alist = [54, 26, 93, 17, 77, 31, 44, 55, 20]

    print(alist)

    quick_sort(alist, 0, len(alist) - 1)

    print(alist)